Commercially available sodium hypochlorite solution (household bleach) is an inexpensive germicide. Diluted 1;10 with water, or even 1:100, it is effective against many disease organisms. The 1:10 dilution meets Center for Disease Control (CDC) recommendations for an AIDS virus disinfectant, acting to kill the virus on laboratory and other work surfaces in as little as one minute.
However, there is a practical problem in that such dilutions can quickly lose strength. Current recommendations are to prepare solutions fresh daily. Such replacement is inconvenient and adds considerable expense when spray bottles or other containers of disinfectant are to be kept continuously ready at several work locations. The present invention is directed to avoiding this problem by providing a dilute hypochlorite disinfectant solution which retains virtually full strength over a year or more.
In the past, various additives and formulations for stabilizing dilute sodium hypochlorite have been tried. (For a listing, see U.S. Pat. No. 4071463.) While some of these may help, even the more effective known formulations provide a stability at room temperature measured by a halflife of at most a few months. This, though adequate for many purposes, falls far short of providing a degree of stability optimum for laboratory disinfectants intended to be shelved in containers for a long period and then put in service and dispensed repeatedly in daily use. For this purpose, the disinfectant should retain at least 75 percent of its hypochlorite content for a period of many months, even years.
Another difficulty with known stabilized dilute hypochlorite disinfectants is that the stabilization has been unreliable, sometimes differing significantly from batch to batch. This variation is attributed, though not with certainty, to the random but nearly unavoidable presence of heavy metal ions in varying trace amounts (parts per million) in the water sources and containers used in formulating and storing the hypochlorite. Such ions, e.g. copper, nickel, and cobalt, are known to accelerate the decomposition of hypochlorite. It is difficult to exclude minute traces of them reliably and completely from formulations, even by conventional deionization of the diluent water, since contact with metal surfaces during manufacture or with impurities in formulative additives can provide ingress of heavy metals. It has been proposed that adding a chelating agent to the water source or disinfectant formulations may improve hypochlorite life by deactivating whatever trace heavy metal ions may be present. Unfortunately, hypochlorite is a sufficiently strong oxidizing agent that it degrades most available chelating agents, making them ineffective.
To summarize, stabilization of dilute hypochlorite bleach to an extent adequate to provide a long-lived laboratory disinfectant has continued as a largely unsolved problem.